Compton Gamma Ray Observatory Status Report #206 Wednesday, Oct. 15, 1997 Questions or comments can be sent to Chris Shrader at the CGRO-SSC. Phone: 301/286-8434 e-mail: shrader@grossc.gsfc.nasa.gov for more info see: http://cossc.gsfc.nasa.gov Guest Investigator News Cycle 7 begins in one month. All notification reports and evaluation summaries were sent to proposers last month. The viewing plan has been completed and will appear shortly on the CGRO-SSC WWW pages. There are a number of OSSE observations for which no secondary target from among our approved targets list could be scheduled. To fill these gaps, we are soliciting "mini-proposals" for targets which may be observable by OSSE during one of these periods without any Z-axis re-orientation. Appended to this message is a set of instructions on how to submit such a proposal. Budget requests associated with approved Cycle-7 are due at the CGRO- SSC now. Also appended to this report is a copy of the first announcement for the 3rd INTEGRAL workshop, entitled "The Extreme Universe", to be held in September 1998. Instrument Team Reports EGRET Viewing period 630, just concluded, was the last planned observation with EGRET in Cycle 6. The Cycle 7 plan calls for 22 weeks of observation in the narrow field mode. The last full gas exchange was made in September, 1995, and since then, the spark chamber operations have been approximately half time in the restricted field mode. Approximately one-half of a gas fill remains in the supply tanks, and this will be used sparingly to maintain the vessel pressure and to do a partial exchange at a later date. Based on the rate of triggers, the expected lifetime should extend beyond what is planned for Cycle 7. The energy calorimeter (TASC) continues to operate full time by periodically sampling spectra in the range from 1 to 200 MeV. Recent Science Highlights from EGRET: Significant optical brightening of the blazar, BL Lacertae led to a Target of Opportunity observation by GRO on July 15-22, 1997. EGRET observed a time-varying emission that peaked in the fourth day, and had decreased by the time of the optical peak. At maximum, the intensity was over 4 times that of the only other detection made in 1995 and more than an order of magnitude greater than summed phase 1 through 3 upper limit value. The photon energy spectrum was distinctly harder in the recent observation. A paper by Bloom et al. reporting these results has been accepted for publication in the ApJ Letters. Recent observations extended the time base for studying the possible long-term variation in the ratio of intensity in the two phase peaks (the P2/P1 ratio) of the Crab pulsar. Earlier Cos-B measurements (Wills et al., 1982, Nature, 296, 723.) suggested a ~14 year sinusoidal cycle in this ratio possibly due to a nutation in the Crab magnetic pole. EGRET measurements in Cycles 1 through 3 were consistent with this possibility. Now with recent observations at a time when the ratio would have varied significantly had it been sinusoidal, EGRET shows that the ratio is consistent with no variation at a significance level of 6 sigma. A paper by Tompkins et al. reporting this result appeared in the September 20 issue of the Astrophysical Journal. A third result was just accepted for publication in the Astrophysical Journal in a paper by Sreekumar et al. It reports on the extragalactic diffuse emission. The spectrum of the diffuse emission is shown to be a power law extending to 100 GeV. This is well beyond the energy region where any of the AGN's have been observed. The lack of a spectral break at high energies has interesting implications for the diffuse emission being a superposition of unresolved AGN sources since the limited blazar observations that extend to TeV energies (Mrk 421 and Mrk 501) indicate the existence of spectral breaks somewhere between 10 and 300 GeV. A paper by Dingus et al. at the recent Cosmic Ray conference demonstrated that for known burst times, using all events that trigger EGRET, rather than just those that satisfy accepted gamma ray criteria, adds significantly to the time profile and even to the spectral evolution information that obtained by the TASC. A sample of three burst events were used in this study, including the recent July 4, 1997 event. This work also demonstrates that EGRET can provide a useful measure of high energy (>100 MeV) emission in bursts even without the use of the spark chamber. OSSE OSSE operations are currently normal. The instrument is working as designed, with all subsystems in complete and full operation. There has been no need yet to activate any of the redundant systems. ---- Proceedings of Fourth Compton Symposium ---- The proceedings of the Fourth Compton Symposium have been sent to the publisher (the American Institute of Physics) and are in production. A publication date of 15 December 1997 is scheduled. The complete reference for the proceedings is: ...in "Proceedings of the Fourth Compton Symposium," 1997, ed. C. D. Dermer, M. S. Strickman, and J. D. Kurfess, AIP Conf. Proc. 410 (New York: AIP). The table of contents of the Proceedings of the Fourth Compton Symposium can be found at . The proceedings are divided into two parts. Volume 1, entitled "The Compton Observatory in Review," consists of 30 chapters devoted to all facets of extraterrestrial Compton science. Note may be made of the articles on gamma-ray line emission from galactic radioactivity by R. Diehl and F. Timmes, on Compton solar gamma-ray observations by G. Share, R. Murphy, and J. Ryan (of particular interest as we head into the peak of the next Solar cycle), and on Compton observations of isolated neutron stars by D. Thompson, A. Harding, W. Hermsen and M. Ulmer. This volume contains a review by M. Finger and T. Prince of accretion-powered pulsars following six years of BATSE and Compton data, and two chapters which summarize the high-energy data (J.E. Grove, J. Grindlay, B. Harmon, X.-M. Hua, D. Kazanas and M. McConnell) and multifrequency connections (S. Zhang, I. Mirabel, B. Harmon, R. Kroeger, L. Rodriquez, R. Hjellming and R. Rupen) of galactic black-hole binaries. This volume also features reviews of the EGRET unidentified sources by R. Mukherjee, I. Grenier and D. Thompson, of the bursting X-ray pulsar GRO J1744-28 by C. Kouveliotou and J. van Paradijs, and nuclear deexcitation gamma-ray lines by H. Bloemen and A. Bykov. It contains much, much more besides! Volume 2, entitled "Papers and Presentations," contains over two hundred articles related to Compton Observatory science. Papers covering results from the RXTE, Beppo-Sax (including an overview by L. Piro) and ASCA satellites, from the Whipple and HEGRA ground-based gamma-ray observatories, and from multiwavelength campaigns are also included here, in addition to new results and discoveries of the Compton Observatory. Our present knowledge of the high-energy universe is displayed in all its richness and variety in these pages. For more information, please contact the editors at NRL. ---- Recent results, publications, and presentations ---- Following an optical flare from BL Lac, a target of opportunity observation was performed by GRO. We reported preliminary OSSE results, a rare detection of a BL Lac object in the OSSE band, in IAU circular 6705, reproduced here: J.E. Grove and W.N. Johnson (Naval Research Lab), on behalf of the OSSE team, report: "We have detected emission from BL Lac between 50 keV and 300 keV with the OSSE instrument on the Compton GRO. For the period 15.7-21.0 July 1997 (UT), the flux in this energy band is (9.0+-1.4)x10^-4 photons cm^-2 s^-1. There is no evidence for variability. The power-law spectrum is hard, with energy index 0.5 (+-0.7, 95% confidence). Although OSSE has not previously observed BL Lac, objects in this class are not generally detected in this energy range." OSSE team members were lead authors on four review papers for the Compton Symposium. Each summarizes the current state of observations of a class of objects by the Compton Observatory and the broad theoretical implications these observations have on high energy astrophysics: "Solar and Stellar Gamma Ray Observations with Compton" by G.H. Share, R.J. Murphy, and J. Ryan. "Galactic Black Hole Binaries: High Energy Radiation" by J.E. Grove, J.E. Grindlay, B.A. Harmon, X.M. Hua, D. Kazanas, and M. McConnell. "CGRO Studies of Supernovae and Classical Novae" by M.D. Leising. "Seyferts and Radio Galaxies" by W.N. Johnson, A.A. Zdziarski, G.M. Madejski, W.S. Paciesas, H. Steinle, and Y.C. Lin. "The Orbital Ephemeris and X-Ray Light Curve of Cyg X-3" (Matz et al.) will appear in the Compton Symposium proceedings. Matz derived a new and current soft X-ray orbital ephemeris for Cyg X-3 using XTE ASM data, and compared the soft X-ray phase and light curve shape to the hard X-ray (>50 keV) light measured by OSSE. There is evidence for a phase shift or light curve shape change between 2--10 (ASM) and >50 keV (OSSE). This paper (including ephemeris) is on astro-ph as paper 9708201. We presented two posters at the recent Huntsville Gamma-Ray Burst Symposium: "High-Energy Spectral Evolution in Cosmic Gamma-Ray Bursts", G. H. Share and S. M. Matz, examined the spectral evolution of a large sample of gamma-ray bursts above several MeV in both SMM and OSSE data, and compared results to standard evolution seen at lower energies. "Search for GRB Afterglow above 50 keV", S. M. Matz, G. H. Share, J. E. Grove, and W. N. Johnson. OSSE has detected significant persistent emission above 50 keV in several gamma-ray bursts, including GRB 970827 which we observed starting 34 s after the trigger using the prompt BATSE/OSSE on-board slew capability. Three strong events showed significant emission extending after the main burst (~10--1000 s) and declining roughly like the observed soft X-ray afterglows seen in other bursts. These detections may help in understanding the relation between the extended afterglows and the bursts themselves. Preprints are available under the OSSE Web site, which has recently undergone a major facelift. The content of the preprint page is being updated, and to simplify downloading, PDF as well as PS versions of preprints and figures will be available. See . ---- Recent observations ---- Recent observations are listed in the following table. 623.5 15-22 Jul BL Lac (public TOO) Mrk 376 (public) 623 22 Jul - 5 Aug GPLANE 215 (J. Skibo) NGC 4388 (J.E. Grove) M87 (J.E. Grove) 625 5-19 Aug GRS 1758-258 (E. Liang) IC 4329A (J.E. Grove) 615.1 19-26 Aug GC region (W. Purcell) NGC 4388 (J.E. Grove) M87 (J.E. Grove) 626 26 Aug - 2 Sep LMC X-3 (J. Kurfess) Vela X-1 (public) 627 2-9 Sep PSR 1055-52 (J. Cordes) NGC 3516 (R. Svensson) q Engineering test data 628 9-16 Sep LMC X-3 (J. Kurfess) Engineering test data 629 16-23 Sep Engineering test data LMC X-1 (J. Kurfess) 630 23 Sep - 7 Oct PSR 1055-52 (J. Cordes) NGC 3516 (R. Svensson) Engineering test data 632.1 7 Oct - (3 Nov) NGC 4945 (G. Madejski) NGC 4151 (J.E. Grove) NGC 4388 (public) 3C 273 (public) ---- Bursts, flares, and transients ---- Bursts, flares, and transients through October 5, 1997 (BATSE triggers 6293 to 6413) have been processed. There were three prompt slews to GRB positions in this period: GRB 970704, GRB 970827 (BATSE trigger 6349), and GRB 970930 (trigger 6404). The first OSSE pointed observations of GRB 970827 started (on source) about 34 sec after the trigger, and the tail of the burst (duration = 200 sec, according to BATSE) was clearly detected in the low range of detector 2. This is the first time we have detected late burst emission in a slew observation. Analysis of the persistent hard X-ray emission from this burst and two others was presented at the Huntsville burst meeting in September. Trigger 6293 (GRB 970704) produced the highest peak flux ever observed in the OSSE shield data, 35800 cts/16 ms (>2 million counts/sec) above background. The previous brightest burst for OSSE was trigger 2151 (GRB 930131, the "Superbowl burst") with about 34600 cts/16 ms. (The third brightest event has only about 11000 cts/16 ms.) Trigger 6293 was the third brightest event ever for BATSE on the 64 ms time scale. The single peak of 6293 is short (~0.144 s FWZI) but well-resolved in our data. The new bursts are available on the WWW at Longer time scale histories of bursts from the TSF shield data are now available on the WWW in a crude form (plot only, no data file) as a link from the individual burst plot pages. We hope to improve the format and accessibility of these data in the near future. ---- Data deliveries ---- Low-level OSSE data products through viewing period 523 and high-level products through viewing period 425 are awaiting delivery to the Compton GRO Science Support Center archive. In addition, by special request all subsequent public Cyg X-1 data sets, both low and high level, have been delivered, as have public data and high-level products from the Mrk 501 TOO (vp 617.8) and the BL Lac TOO (vp 623.5). Refer to the GROSSC page on the WWW , or contact Tom Bridgman (bridgman@grossc.gsfc.nasa.gov) for more information. COMPTEL The COMPTEL instrument is functioning normally. No unusual problems arose since the last status report. The instrument is now being supported by a new Instrument Ground Station. This ground station interfaces with the new PACOR2 system. It has considerably more capability that the old system, collecting a larger fraction of real time data for the purpose of assessing instrument health and safety. Instrument commanding will migrate to the new system on October 20. Because of reduced manpower and the increased capability of the new system, operations have been reduced to a single shift/day. There have been no significant burst detections in the COMPTEL field-of-view since the burst of August 7 1997. Although there have numerous alerts, none has exhibited significant emission above 1 MeV in the 1 sr field-of-view. The COMPTEL background has increased since the reboost to 520 km. The background rate after standard data cuts has risen significantly, depending upon location in the orbit and time since the last SAA exit, entirely below 4 MeV. At times after exiting the SAA, the raw count rate exceeds the telemetry capacity, thereby reducing the instrument live time. The scientific impact of the increased background is being assessed and palliative steps may be taken to ameliorate the deleterious condition. The COMPTEL team meeting will be held at Utrecht from October 14 to October 17. Two papers have been accepted for publication in A&A: COMPTEL observations of Centaurus A at MeV energies in the years 1991 to 1995, Steinle et al. COMPTEL observations of the quasar PKS 0528+134 during the first 3.5 years of the CGRO mission, Collmar et al. Papers to be presented at the AAS HEAD meeting in Estes Park, Colorado Nov. 4-7,1997: COMPTEL Spectra of the Galactic MeV Emission, Bloemen et al. The Instrumental Background of COMPTEL, Weidenspointner et al. COMPTEL Measurements of the Cosmic Diffuse Gamma Ray Emission, Kappadath et al. Papers presented at the Fourth Huntsville Gamma Ray Burst Symposium, September 15-20, 1997: Analysis of COMPTEL GRB Locations, Kippen et al. MeV Measurements of GRBs by CGRO-COMPTEL, Connors et al. Papers presented at the 25th International Cosmic Ray Conference, Durban, SouthAfrica, July 30-August 6, 1997: COMPTEL Observations of 3C279 During the First Four Years of the CGRO Mission, Collmar et al. MeV Measurements of Gamma Ray Bursts by CGRO-COMPTEL, Connors et al. COMPTEL All-Sky Imaging at 2.2 MeV, McConnell et al. A Search for Gamma Ray Emission from the Quiet-Time Sun, McConnell et al.Neutron Transport in the Solar Atmosphere, C.A. Young et al. The Solar Flare Event on 15 June 1991, Rank et al. Extended Gamma Ray Emission of the Solar Flares in June 1991, Rank et al. Detection of the COS-B/EGRET Source GRO J2227+61, Iyudin et al. BATSE Burst Studies: The Fourth Huntsville Gamma-Ray Burst Symposium was held on September 15-20, with about 200 scientists in attendance. Much of the program was devoted to the recently discovered X-ray, optical, and radio counterparts. The proceedings will be published by the AIP. Papers published recently: "BATSE Gamma-Ray Burst Line Search. V. Probability of Detecting a Line in a Burst", D. Band et al. ApJ, 485, 747 (1997). "The Cosmological Signatures and Flux Distributions of Gamma-Ray Bursts with a Broad Luminosity Distribution", J. Brainerd, ApJ, 487, 96 (1997). In October, a report was submitted to the IAU describing two intense bursts characteristic of SGRs (IAU Circular 6743). An IPN localization using CGRO, Ulysses, and KONUS-WIND indicates that the source is a new SGR (SGR1815-14). Occultation Studies: The BATSE galactic plane monitoring effort has revealed hard X-ray emission from the X-ray burst source GS 1826-238 (IAU Cir. 6611). The galactic plane monitor utilizes the Earth occultation imaging technique and CFA-Harvard BATSE Image Search (CBIS) to scan the galactic plane region out to +/-20 deg latitude. GS 1826-238 was known as a hard X-ray emitter from OSSE observations (see Strickman et al. A&AS 120 C 217-220), but its character as a persistent or transient source was not known. A preliminary light curve indicates the source to be persistent over the Aug 1996-97 time interval at an average flux of about 45 mCrab in the 20-100 keV band. The reported RXTE/ASM flux (2-10 keV) is about 26 mCrab from Sep 1996 - Aug 1997. Accreting Pulsar Studies: In the last three months, the BATSE pulsed source monitoring program has detected the accreting pulsars Her X-1, Cen X-3, 4U 1626-67, OAO 1657-415, GX 1+4, Vela X-1 and Cep X-3. Results from these observations are available at http://www.batse.msfc.nasa.gov/data/pulsar/histories.html. Her X-1 was observed for three main-on states. Cen X-3 was spinning up in July and early August, but from August 11 to October 1 it was in a low flux state and was not detected by BATSE. When it reappeared it was at a higher spin frequency, but had started to spin down. The eclipsing binary pulsar OAO 1657-415 has been spinning down. It brightened in late August, with current pulsed fluxes near 25 mCrab (20-50 keV). GX 1+4 was detected for much of July and August, with typical pulsed fluxes of 50 mCrab. In September it dropped in flux to typically 15 mCrab, and is currently being detected only intermittently. Pulsed fluxes from Vela X-1 have been typically 125 mCrab. An outburst from the transient pulsar Cep X-4 was seen in July. This was a fairly weak outburst peaking about 15 mCrab pulsed flux (20-50 keV). ------------------------------------------------------------------------------- CGRO Cycle 7 Miniproposal Opportunity Due to a number of observing constraints on the OSSE (Oriented Scintillation Spectrometer Experiment) instrument, there are ten viewing periods (a total of 11 observing weeks) where we have no secondary target. We have opened up a "mini-proposal" opportunity for this time. No funding is being offered, just observing time, again subject to some constraints. There are now 10 viewing periods available (in principle) for miniproposals: 708(1 week) , 709(1 week), 710(1 week), 711(1 week), 714(1 week), 715(1 week), 719(1 week), 727(2 weeks), 732(1 week), 737(1 week). Proposal Guidelines: -------------------- * The deadline for proposals is December 8, 1997. * Proposals should be submitted by e-mail to: bridgman@grossc.gsfc.nasa.gov Targets Selection Constraints: ------------------------------ * Target will be classed as secondary (which means it obtains the smaller share of exposure time compared to the primary target). Depending on the orientation of the OSSE scan plane, the Earth, and the position of the primary target, it is possible to get as much as 30 minutes of exposure per orbit. An optimum observation should have at least 15 minutes of exposure. This can be tested with the VSTAT program (contact Tom Bridgman for details). * The target must not be already proposed in Cycle 7, nor fall in detector scan range covered by currently scheduled OSSE scanning/mapping observations. * You must specify the coordinates of the target, either Galactic or RA and Dec (Epoch 2000). * NO changes in the spacecraft orientation are permitted. * You can propose for multiple Viewing Periods in a single proposal. If several viewing periods can reach a single target, you might want to try that combination. * Proposal page limit is 2 pages (120 80-character lines). Text, LaTeX (no custom style files!!) or PostScript is permitted. * The target must lie within 2 degrees of OSSE scan plane. You can use the graphical tool at http://cossc.gsfc.nasa.gov/cossc/osse/minicycle7.html to run a preliminary check of your targets. Proposals will be judged based on the ability to satisfy the above conditions and on scientific merit. This might be a worthwhile opportunity for a faculty member or even a student who would like to work with gamma-ray observations. If you, or anyone you know, might be interested in this opportunity, I ask that you forward this message to them. If you have any questions, please contact Tom Bridgman at bridgman@grossc.gsfc.nasa.gov Other items of interest: -------------------------------------------------------------------------- A conference entitled "Observing the Highest Energy Particles (>10**20 eV) From Space" will be held at the University of Maryland on November 13-15. Contact Robert Streitmatter (streitmatter@lheavx.gsfc.nasa.gov) for more info). -------------------------------------------------------------------------- 3rd INTEGRAL Workshop `THE EXTREME UNIVERSE' 14 - 18 September 1998 San Domenico Palace Hotel Taormina/Sicily, Italy Point of contact: Angela Bazzano Istituto di Astrofisica Spaziale, C.P. 67, 00044 Frascati (Roma), Italy e-mail: tao98@ias.fra.cnr.it http://www.ias.fra.cnr.it/ias-home/imager/tao98.htm or http://astro.estec.esa.nl/SA-general/Projects/Integral/integral.html Purpose: The International Gamma-Ray Astrophysics Laboratory INTEGRAL is ESA's gamma-ray mission (in collaboration with Russia and NASA) of the long term space science programme `Horizon 2000'. INTEGRAL - using high-resolution gamma-ray spectroscopy, coded aperture fine imaging with concurrent X-ray and optical source monitoring - will be launched in April 2001. The observatory will be operated for two to possibly five years. The majority of observing time will be given to the scientific user community through a single peer review process. The main goals of this`The Extreme Universe 3rd INTEGRAL workshop ' will be to discuss recent progress in hard X-ray and gamma-ray astronomy on compact objects and to put these results in a broader perspective of astrophysics in general. Furthermore this workshop will provide the opportunity to also discuss latest scientific results compatible with all INTEGRAL scientific objectives. The status of the INTEGRAL mission, instruments and plans for the observing programme with INTEGRAL will also be presented. This third INTEGRAL workshop builds upon the results of the earlier ones held in 1993 and 1996: 1st INTEGRAL workshop `The Multi-Wavelength Approach to Gamma-Ray Astronomy' Les Diablerets, Switzerland, 1993. Proceedings: ApJ Suppl.Ser. Vol. 92, Number 2, pp. 325 - 698 (June 1994). 2nd INTEGRAL workshop `The Transparent Universe' St Malo, France, 1996. Proceedings: ESA SP-382 (March 1997) It is planned to cover the following topics by invited papers, contributed papers and posters: (1) Compact variable sources (Black hole candidates, neutron stars, Novae and Supernovae, superluminal and radio jet sources) (2) Nucleosynthesis and diffuse gamma-ray emission (3) AGN, Seyfert galaxies and Blazars (4) Normal galaxies and clusters of galaxies (5) Surveys and high energy background radiation (6) Gamma-ray bursts and soft gamma-ray repeaters